The present invention relates to a toe cap for a protective shoe and, more particularly, to an injection molded plastic toe cap.
For many years, toe caps for protective shoes have been made of thin steel sheets formed into shoe toe-shaped bodies which are sewn or otherwise attached on the inside of the leather toe cap of a shoe or boot. Steel toe caps are known to deform under vertically applied compressive or impact loads and to undertake a permanent set which, if excessive, may result in a crushing and/or cutting injury to the toes of the wearer. Attempts have been made more recently to substitute various plastic materials for steel in safety toe caps and number of prior art patents show such constructions.
My prior U.S. Pat. Nos. 5,210,963 and 5,331,751 disclose injection molded plastic toe caps which utilize a fiber-filled plastic resin and are formed in a manner to optimally orient the reinforcing fibers to enhance the strength of the toe cap. These patents also disclose special structural shapes for strength optimization and controlled vertical collapse under load, as well as optimal molding parameters.
U.S. Pat. No. 4,735,003 discloses a molded plastic toe cap which may be made from a variety of thermoplastic and thermosetting resins, both with and without fiber reinforcement. Various molding techniques, including injection and compression molding are disclosed.
British Patent Application No. 2,138,272A also discloses a protective toe cap made from an injection molded glass-filled plastic material. European Patent Application No. 83304046.2 describes a protective toe cap for a shoe which is compression molded from a plastic material that is reinforced with uniaxially aligned continuous fibers extending laterally across the roof of the cap.
In the United States, suitability of toe caps for new protective footwear is determined in accordance with American National Standard for Personal--Protection Protective Footwear (ANSI Z41-1991). This Standard provides, inter alia, for separate compression and impact tests, both of which apply vertical loads to the roof of the toe cap actually installed in a shoe or boot. Similar but somewhat more rigorous standards are applicable in Canada under Canadian Standards Association toe impact test Z-195 March 1984. In Europe, the test regimen is dictated by DIN standards.
The rigorous test regimens to which protective toe caps are subject has it made extremely difficult to design and build a toe cap of either steel or plastic which will consistently meet any one of the standards, much less all of them. The problem is exacerbated by variations in toe cap styles in the United States and between the United States, Canada and Europe. These styles are, in turn, dictated to some extent by variations in the styles and in the construction of shoes, both work shoes and dress shoes which are modified to include protective toe caps. There is also a desire in the industry to eliminate steel toe caps for reasons in addition to those mentioned above, such as the heat and electrically conductive properties of steel. Also, the response of steel to magnetic fields or electrical signals makes it undesirable for certain military and the like applications.
Notwithstanding the improvements in plastic materials, molding techniques, and specific structural modifications, it has still proven to be a difficult engineering challenge to meet the rigorous standards for protective footwear as discussed above. Extensive testing of plastic toe caps molded to the shapes shown in the prior art patents discussed above suggests that subtle changes in dimensions and contours can have a significant effect on the ultimate strength of the toe cap and its ability to meet the compression and impact tests. On the other hand, it is desirable to minimize the plastic material used and therefore minimize the weight. It has also been found that there is a significant interrelationship between the protective plastic toe cap and the other materials from which the shoe is made, particularly the material for the inner sole. As a result, it would be desirable to have a molded plastic toe cap which, if constructed to certain minimum dimensions and using a variety of suitable plastic materials, would provide a toe cap strong enough to meet the safety test standards yet be small and light.